Field of the Invention
The present invention relates to a toner for use in electrophotographic systems, electrostatic recording systems, electrostatic printing systems and toner jet systems.
Description of the Related Art
As electrophotographic full-color copiers have become popular in recent years, there has been increasing demand for higher printing speeds and energy savings. To achieve higher printing speeds, techniques are being investigated for melting the toner more rapidly during the fixing process. Further, to save energy, techniques are being investigated for fixing the toner at lower fixation temperatures so as to reduce power consumption during the fixing process.
Recently, toners containing crystalline polyester resin in the binder resin have been developed as a way of improving the low-temperature fixability of the toner. By including a crystalline polyester in the toner, it is possible to improve storage stability and durability because the toner melts rapidly at the fixation temperature but maintains its hardness up to the fixation temperature.
Because adding a crystalline polyester to a toner confers various properties on the toner including a sharp melt property, various techniques have been proposed for exploiting the advantages of these properties or minimizing their disadvantages.
Japanese Patent Application Publication No. 2003-270856 discloses a toner manufacturing technique exploiting the sharp melt property, and describes a method for obtaining a toner with a high degree of circularity by including a crystalline polyester and heat treating the toner, resulting in a toner with excellent transferability.
In Japanese Patent Application Publication No. 2012-63559 a crystalline polyester dispersing agent is used in addition to the principal binder resin and crystalline polyester, and the solubility parameters of each are defined. The object here is to reduce exposure of the crystalline polyester on the toner surface layer, and finely disperse the crystalline polyester in the interior of the toner particles, thereby controlling toner filming on other members and improving hot offset resistance.
Japanese Patent Application Publication No. 2012-18391 proposes a toner containing a finely dispersed crystalline resin, in which the surface layer of the toner particles is covered with an amorphous resin. Heat-resistant storage stability and durable stability are thus achieved in a toner with excellent low-temperature fixability containing a crystalline polyester.
Japanese Patent Application Publication No. 2011-145587 proposes improving fixing separability by stipulating the relationship between the cross-sectional area of the crystal domains of the crystalline polyester and the cross-sectional area of the domains of the release agent in a toner. The speed at which the wax seeps to the surface of the toner is thus optimally balanced with the melting speed of the toner binder resin, resulting in both low-temperature fixability and good fixing separability.
Japanese Patent Application Publication No. 2004-279476 proposes improving hot offset resistance by giving the crystals of the crystalline polyester in the toner a major axis diameter of at least 0.5 μm and no more than ½ the diameter of the toner.
In Japanese Patent Application Publication No. 2011-197274, low-temperature fixability is improved by distributing the crystalline polyester preferentially as a lamellar layer on the surface of the toner.
As illustrated by the techniques disclosed here, the properties of a toner are greatly affected by the state of the crystalline polyester in the toner, and controlling this state is one of the important techniques for maximally exploiting the performance of the crystalline polyester. These disclosures also suggest that when a crystalline polyester is present in the surface layer of a toner in particular, there is be a trade-off between advantages in terms of fixability and the like and disadvantages in terms of durability. There is therefore demand for toner technology whereby the toner properties other than fixability can be improved while taking advantage of the superior fixability provided by the crystalline polyester.